Re: paravirtualization status

Avi Kivity
2007-05-13T11:54:00Z

Omar Khan wrote:
> hi,
> What is the status of paravirtualization?

It's basically stalled.

However, I'd like to restart this, on a much bigger scale. Using
paravirt_ops, one can use direct paging (like Xen) instead of shadow
paging, and achieve better performance. In fact, it should be faster
than Xen as, on one hand, syscalls are fast (esp. with 64-bit guests),
and on the other hand, there's very little mmu overhead.

> Also when Ingo released his
> paravirtualization patch and some results Avi noted that :
>
> "Very impressive! The gain probably comes not only from avoiding the
> vmentry/vmexit, but also from avoiding the flushing of the global page
> tlb entries." [http://thread.gmane.org/gmane.linux.kernel/481084]
>
> can someone please explain briefly what the "global page tlb entries" are?
>

When the kernel switches context to another process, it flushes out the
tlb (a cache of translations of virtual addresses to physical
addresses). An optimization is not to flush cached translations of
kernel virtual addresses, since these are the same for all processes in
Linux. Such translations are marked as 'global', indicating to the cpu
that they need not be flushed on a context switch.

--
error compiling committee.c: too many arguments to function

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